Finally, empirical data suggests that assets are sold much more slowly during retirement years than when they are accumulated during working years. - Didier Sornette

The acceleration of the number of traders buying into the market in the inflating bubble captures the oft-quoted observation that bubbles are times when the "greater fool theory" applies.

The same basic ingredients are found repeatably: fueled by initially well founded economic fundamentals, investors develop a self-fulfilling enthusiasm by an imitative process or crowd behavior that leads to an unsustainable accelerating overvaluation.

The assumption of perfectly rational, maximizing behavior won out until recently in the art of modeling, not because it often reflects reality, but because it was useful.